While it stands excellently written, well executed, visually pretty, and intriguing, it can dull. Fun but dull.
The sandbox world you're given is broad and bold, though a bit drab, considering it's cactus, rocks, and dirt almost as far as the eye can see. The sheer scope of the world, however, makes up for its lack of diversity; while the world feels big, it's not impossible to traverse it, and there are enough hunting side-quests and different minigames that allow you to explore the land at your leisure; furthermore, the desert atmosphere does carry a unique charm. The plot and characters all carry themselves with that cowboy swagger you'd expect to see in any Western, and deliver with clichés firmly lassoed and corralled in all the expected places with well acted and written dialogue.
As for the gameplay, it handles excellently, with heated gun battles and horse race chases, though given this is the entire basis of the game, it at times gets a bit old and boring. While other quests such as collecting wild herbs and hunting wild animals exist, they never seem to balance the main missions, and nobody in their right mind could have thought that missions involving you herding cows could have been a good idea when the cows have the frequent habit of impaling themselves on trees, getting lost on railroad tracks in front of oncoming trains, or diving headfirst off cliffs.
While Red Dead Redemption offers much exploration and a very well written plot, the substance seems a bit sparse. Many of the missions seem to exist simply for the sake of doing something, and it takes 10 minutes just to listen to the characters drone on about their lives before the mission even starts, before spending the next 10 minutes trotting alongside them as they whine about their woes to you until you reach your destination. The game is excellently written and a barrel of fun, but it all seems almost forced and meaningless in the end, leaving you with a feeling emptiness and expectations unfulfilled. Regardless, the game is definitely worth a play through, and won't leave you regretting your time. Except the time you spend herding cows.